1. Technical Field
This invention relates to voice processing. In particular, with methods of speeding-up or slowing down speech messages.
2. Background Art
Sped speech, or variable speed speech usually denotes a means to either slow-down or speed-up recorded speech messages without altering their quality.
Such means are of great interest in voice processing systems, such as voice store and forward systems, wherein voice signals are stored for play-back later on at a varied, speed. They are particularly useful to operators looking for a specific portion of a recorded message, by speeding-up the play back to rapidly locate the portion looked for, and then slowing down the process while listening to the desired portion of the message. It should be noted that speed varying might conventionally be achieved with mechanical means whenever speech is stored in its analog form on moving memories. However, this would distort the signal pitch and, in addition, it would not apply to digital systems wherein speech is processed digitally.
A sophisticated method for implementing sped speech has been proposed by M. R. Portnoff in IEEE Trans. on Acoust., Speech and Signal Processing, Vol. ASSP 24, No. 3, pp. 243-248, June 1976 (Implementation of the digital phase vocoder using the Fast Fourier Transform). This method is based on adaptive measurement of the pitch period, and insertion or deletion of speech samples on a pitch period basis. This technique requires the accurate estimation of the pitch period, which is both complex and expensive to achieve, especially in applications involving telephone signals wherein the low part of the frequency bandwidth (0-300 Hz) including the pitch has been removed.